king is right...

If you have the A/C on, the fan should be running at "slow speed"... once the needle gets just above halfway, it should speed up.

Deb walker had the same problem... turned out to be the fan motor. She found one on eBay for around $150 -included the shroud, blades, motor and harness.

It could be the 50 amp fuse or the fan module itself.